The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Wireless networks are put under an ever increasing pressure to provide more throughput using a limited spectrum. The recent trend to increase the nominal capacity has been essentially to increase the number of MIMO (Multiple Input Multiple Output) spatial streams, and use larger channel widths, up to 40 MHz for the IEEE 802.11n standard and up to 160 MHz for the IEEE 802.11ac standard.
Off-the-shelf IEEE 802.11 hardware can be configured to adapt the channel width or the transmit power or the channel center frequency. Each of these three parameters has a large impact on both the performance and the interference created on neighboring links.
The channel width determines the amount of spectrum that they consume, the transmit power relates to the intensity of this spectrum usage and the channel center frequency determines where they operate in the available spectrum band.
These different parameters have usually been considered in isolation, even though they are tightly coupled and strongly interacting. All of them influence, usually in complex ways, the amount of interference as well as the capacity experienced by interfering wireless links.
Usually, for an isolated link having a large enough SNR (Signal to Noise Ratio), the effective capacity grows approximately linearly with the channel width, and increasing the latter is beneficial.
However, the total amount of available spectrum is finite, and using larger channel widths increases the likelihood that two neighboring links use overlapping portions of the spectrum. Indeed, it has been observed that using larger channel widths can increase interference to an extent that is detrimental to the effective capacity. For this reason, the current IEEE 802.11n standard can operate using two different channel widths, namely, 20 MHz and 40 MHz, the latter being referred to as channel-bonding.
Thus, there is a need for automated procedures that efficiently select the width of the spectrum interval used by the nodes of a wireless network.
For a given transmit power, adapting the channel width changes the amount of power-per-hertz, which in turn impacts the SNR. In addition, because it takes more time to send a packet using a narrow channel width, this parameter directly impacts IEEE 802.11 CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) channel access arbitration and interference in the time domain.
Using variable transmit powers has been acknowledged as being a potentially efficient way of improving the performance of wireless networks. For isolated links, using as large a transmit power as possible is usually beneficial. However, when several links are present, it may be more efficient to reduce the transmit power of some links, which comes at the price of potentially reducing the effective capacity of these links, in order to reduce their interference range and increase spectral re-use.
Finally, while it is well understood that adapting the transmit power has the potential benefit of increasing the spectral re-use, this parameter is hardly touched in practice, due to potentially detrimental effects. While reducing the transmit power can reduce the interference range of a node, it can also deteriorate the SNR at the receivers, possibly making the node switch to lower physical rates. Because lowering the physical rate increases the airtime consumption, decreasing the transmit power can thus sometimes increase the effective interference of a node on its neighbors.
For both transmit power and channel width, there is therefore a trade-off between the capacity experienced by isolated links, and the amount of interference introduced when several links interfere.
For fixed channel width and power, the influence of channel center frequency has been thoroughly studied in the literature. Whether it is applied in centralized or distributed settings, the problem usually has an unilateral objective, which consists in reducing interference between neighboring wireless nodes. In this case, it is usually beneficial to separate transmissions as much as possible in the spectral domain. When considering multiple widths and transmit powers, these techniques do not capture the corresponding dependence of the link capacities.
There has been some work considering simultaneous channel center frequency and width allocation for IEEE 802.11 networks. A first approach reduced this problem to an efficient packing of time-spectrum blocks, where the goal is to avoid block overlaps both in time and frequency. A second approach proposed a variable-width scheme where highly loaded access points are favored to use more spectrum, so as to introduce a natural load-balancing. However, these approaches neglected much of the complexity of actual interference patterns. A third approach considered an enterprise setting with a central controller, and proposed an algorithm for assigning channel center frequencies and widths. However, its centralized setting restrains this method to enterprise networks.
Some prior art considered channel assignment, i.e. channel center frequency, and transmit power. For instance, Ahmed et al. proposed in “Smarta: a self managing architecture for thin access points”, in Proceedings of the 2006 ACM CoNEXT conference, CoNEXT'06, pages 9:1-9:12, New York, USA, 2006, a method for assigning channels and transmit powers to access points in enterprise networks. In this paper, channel assignment is performed at a slower time scale, then power-level is assigned at a faster time scale. This method targets enterprise setting, where a central network controller is present to decide on the resource allocation.
None of the existing spectrum allocation methods can be applied in current IEEE 802.11-based wireless networks in order to ensure a satisfying end-user quality of experience.